System and method for controlling regeneration of an exhaust after-treatment device

ABSTRACT

A method for controlling regeneration of an exhaust after-treatment device for an internal combustion engine in a vehicle includes establishing a baseline value for a mass of soot collected in the exhaust after-treatment device. The baseline value is a threshold mass of soot to be reached for regenerating the filter, and is determined as a function of a speed of the engine and a quantity of fuel entering the engine. The method also includes modifying the baseline value in response to an engine operating parameter that alters a fuel-air ratio of a combustible mixture entering the engine to generate a modified baseline value. The method additionally includes regenerating the exhaust after-treatment device using the modified baseline value. A system for controlling regeneration of an exhaust after-treatment device for an internal combustion engine is also provided.

TECHNICAL FIELD

The present invention is drawn to a method for controlling regenerationof an exhaust after-treatment device for an internal combustion enginein a vehicle.

BACKGROUND

Various exhaust after-treatment devices, such as diesel particulatefilters and other devices, have been developed to effectively limitexhaust emissions from internal combustion engines. In the case ofdiesel engines, a great deal of effort continues to be expended todevelop practical and efficient devices and methods for reducingemissions of largely carbonaceous particulates in exhaust gases.

One method for reducing such particulate emissions is to providesuitable particulate filters or traps in engine or vehicle exhaustsystems. Such particulate filters are typically adapted to collect anddispose of the sooty particulate matter emitted from diesel enginesprior to discharge of the exhaust gases to atmosphere. Additionally,such filters may be regenerated or cleaned using high temperatureexhaust, which burns particles that may otherwise accumulate and clogthe system.

SUMMARY

A method for controlling regeneration of an exhaust after-treatmentdevice for an internal combustion engine in a vehicle includesestablishing a baseline value for a mass of soot collected in theexhaust after-treatment device. The baseline value is a threshold massof soot to be reached for regenerating the filter, and is determined asa function of a speed of the engine and a quantity of fuel entering theengine. The method also includes modifying the baseline value inresponse to an engine operating parameter that alters a fuel-air ratioof a combustible mixture entering the engine to generate a modifiedbaseline value. The method additionally includes regenerating theexhaust after-treatment device using the modified baseline value.

According to the method, the modification of the baseline value may beexecuted in response to an engine operating parameter that alters thefuel-air ratio by varying the mass of air entering the engine.

The modification of the baseline value may also be executed in responseto an engine operating parameter that alters the fuel-air ratio byvarying a mass of fuel entering the engine.

The mass of fuel entering the engine may be varied in one manner whenthe engine is operating in a steady state and in another manner when theengine is operating in a transient state. Additionally, the mass of fuelentering the engine may be varied by turning on exhaust gasrecirculation in the engine.

Furthermore, according to the method, the modification of the baselinevalue may be executed via a controller. The controller may be programmedwith a look-up table that may include a range for the engine operatingparameter.

A system for controlling regeneration of an exhaust after-treatmentdevice for an internal combustion engine and a vehicle employing such asystem are also provided.

The above features and advantages and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of vehicle with an engine connectedto an exhaust system having an exhaust after-treatment device; and

FIG. 2 is a flow diagram of a method for controlling regeneration of theexhaust after-treatment device of FIG. 1.

DETAILED DESCRIPTION

Referring to the drawings, wherein like reference numbers refer to likecomponents throughout the several views, FIG. 1 schematically depicts avehicle 2. Vehicle 2 includes a system 8 configured to controlregeneration of an exhaust after-treatment device 24. System 8 includesan internal combustion engine 10 connected to an air intake system 12.Air intake system 12 is configured for delivering an ambient air flow 14to the engine for subsequent combining with an appropriate amount offuel into a combustible mixture entering the engine 10. The temperatureof the air flow 14 entering engine 10 is monitored by a sensor 13.

The air intake system 12 includes a turbocharger 16 for pressurizing theincoming air flow 14, and a charge air cooler 18 for reducing thetemperature of the pressurized air flow in order to improve theoperating efficiency of engine 10. The temperature of the air flow 14following the charge air cooler 18 is monitored by a sensor 19.Turbocharger 16 is energized by an exhaust gas flow 20 that is releasedby engine 10 following each combustion event. The turbocharger 16 isconnected to an exhaust system 22, which includes the exhaustafter-treatment device 24. As shown, the engine 10 is a compressionignition, i.e., a diesel, engine, and the exhaust after-treatment device24 is a particulate filter adapted to collect and dispose of the sootyparticulate matter emitted from the engine prior to discharge of anexhaust gas flow 20 to atmosphere.

The exhaust system 22 includes a diesel oxidation catalyst 26 that isadapted to oxidize and burn hydrocarbon emissions present in the exhaustflow 20. Following the diesel oxidation catalyst 26, the exhaust flow 20passes through a selective catalytic reduction catalyst 28, whichreduces at least some of the nitrogen oxides present in the exhaust flowinto water and nitrogen. After the reduction catalyst 28, the exhaustflow 20 passes into the exhaust after-treatment device 24 through anentrance 30, and then exits the after-treatment device through an outlet32 and continues on to the atmosphere sans the majority of sootparticulates. Although, as shown, the reduction catalyst 28 ispositioned upstream of the exhaust after-treatment device 24, theafter-treatment device may also be positioned downstream of thereduction catalyst without affecting the after-treatment of the exhaustflow 20.

System 8 also includes a controller 34 that is operatively connected toengine 10. Controller 34 is programmed to predict a baseline value forthe mass of soot that collects in the after-treatment device 24 duringoperation of engine 10. The baseline value for the mass of soot is athreshold amount of soot that is allowed to be reached or collected inthe after-treatment device 24 before maintenance or regeneration ofexhaust system 22 is performed. The baseline value in one embodiment maybe established as a function of an operating speed of engine 10 and aquantity of fuel that has entered the engine for combustion. Speed ofengine 10 may be sensed by a sensor 36, while the amount of fuel thathas entered the engine may be sensed by a sensor 38.

The baseline value may be an amount of soot that has been empiricallydetermined to be the level at which maintenance of exhaust system 22should be performed. Maintenance of exhaust system 22 may be achievedeither by active regeneration or by replacing the after-treatment device24. Active regeneration of the after-treatment device 24 may beperformed by changing operating parameters of engine 10 to increasetemperature of exhaust flow 20 to burn the soot that has collected inthe after-treatment device. Accordingly, controller 34 may be programmedto command or trigger the engine 10 to actively regenerate theafter-treatment device 24. Additionally, active regeneration of theafter-treatment device 24 may be performed by a direct injection andigniting of fuel in the exhaust gas flow 20. In such a case, controller34 may be programmed to command the fuel to be injected into the exhaustsystem 22 at an appropriate time.

Controller 34 is additionally programmed to modify by a mathematicalcalculation the baseline value in response to engine operatingparameters that alter a fuel-air ratio of the combustible mixtureentering engine 10. In general, when the fuel-air ratio is increased,the mass of soot collecting in the after-treatment device 24 isincreased. The operating parameters that alter or influence a fuel-airratio of the combustible mixture entering engine 10 may include a changein density of the incoming air flow 14, i.e., an increase or a decreasein the mass of the air entering the engine. A signal indicating a changein density of the incoming air flow 14 may be provided to the controller34 by a sensor 40. Sensor 40 is adapted to detect the ambient airpressure, which may then be correlated to the altitude at which engine10 is operating. Additionally, a signal from a sensor 42 that is adaptedto sense ambient air temperature may be employed to further modify thebaseline value.

The operating parameters that influence a fuel-air ratio of thecombustible mixture entering engine 10 may also include a signalindicating whether the engine 10 is operating in a transient or in asteady state. When engine 10 is operating in the transient state, anadditional amount of fuel may be used for combustion, as compared to theamount of fuel being injected into the engine during the steady stateoperation. The baseline value may be modified to indicate that a largermass of soot is being collected when the engine 10 is operating in atransient state, and modified to indicate that a lower mass of soot isbeing collected when the engine is operating in a steady state. Whetherthe engine 10 is operating in a transient or in a steady state isregulated by the controller 34. A signal indicating the currentoperating state of engine 10 may, therefore, also be provided by thecontroller 34.

The operating parameters that influence a fuel-air ratio of thecombustible mixture entering engine 10 may additionally include whetheran exhaust gas recirculation (EGR) valve 44 is on or off As isappreciated by those skilled in the art, when the EGR valve 44 is on,the fuel-air mixture becomes richer because the re-circulated exhaustgas flow 20 includes unburned fuel which is reintroduced for combustion.Therefore, the baseline value is modified to show an increase in themass of soot collected in the after-treatment device 24 when the EGRvalve 44 is on. The controller 34 is additionally programmed to triggerregeneration of the after-treatment device 24 using the baseline valuethat was modified in response to the sensed variation in the engineoperating parameters that alter the amount of air entering the engine10. In operation, when the current modified baseline value for the massof soot collected reaches a predetermined level, the controller 34provides an output signal that indicates a trigger to performregeneration of the after-treatment device.

Furthermore, controller 34 may be programmed with a look-up table 46that includes ranges of values for the previously described operatingparameters of engine 10 that influence or alter a fuel-air ratio of thecombustible mixture entering the engine. The ranges of values for theoperating parameters of engine 10 that influence or alter a fuel-airratio of the combustible mixture are typically determined empiricallyduring the testing and calibration stages of engine development. Oncedetermined, the variation in such operating parameter values iscorrelated with a variation in the amount of soot mass that is collectedin the after-treatment device 24. Based on the recorded variation in theamount of soot collected, a mathematical factor is derived for eachobserved data point of each operating parameter, representing the effectthat such variation has on the mass of soot collected above the baselinevalue. Additionally, the observed data points for the operatingparameters may be plotted to generate graphical curves and then utilizethe curves to interpolate between data points, thus generatingcontinuous ranges of mathematical factors.

The derived mathematical factors are assembled into a look-up table 46,which is then programmed into the controller 34 for subsequent accessduring actual operation of engine 10. Thus, generally in order todetermine the modified baseline value for the mass of soot collected inthe after-treatment device 24, controller 34 multiplies thepredetermined baseline value by the derived factor(s) whenever thedescribed variation in the engine operating parameter(s) is sensed.Following such modification of the baseline value for the mass of soot,controller 34 triggers the regeneration of the after-treatment device 24to burn off the collected particulates prior to the occurrence of anydamage to the device.

FIG. 2 depicts a method 50 for controlling regeneration of the exhaustafter-treatment device 24 as described with respect to FIG. 1.Accordingly, the method commences in frame 52, where it includesestablishing the baseline value for the mass of soot collected in theexhaust after-treatment device 24 that is to be reached prior toregenerating the filter. As described above, the baseline value for themass of soot may be based on the speed of engine 10, and on the quantityof fuel entering the engine. Following frame 52, the method proceeds toframe 54, where it includes modifying the baseline value for the mass ofsoot collected in response to the engine operating parameter that altersthe fuel-air ratio of the combustible mixture entering engine 10. Thebaseline value for the mass of soot collected may be modified by thecontroller accessing the appropriate derived mathematical factors in thelook-up table 46, as described above.

As described above, the engine operating parameter that alters thefuel-air ratio of the combustible mixture may include a factor thatdrives a change in the density of air that is used by the engine 10 forcombustion. The engine operating parameter that alters the fuel-airratio of the combustible mixture may also include a factor that accountsfor the engine 10 operating either at a steady or at a transient state.Additionally, the engine operating parameter that alters the fuel-airratio of the combustible mixture may include a factor that accounts forwhether the exhaust gas recirculation (EGR) in the engine 10 is on oroff. Controller 34 may be programmed to continuously monitor theappropriate time to trigger regeneration of the exhaust after-treatmentdevice 24 based on the modified baseline value of soot collected.

After the baseline value for the mass of soot collected in the exhaustafter-treatment device 24 has been modified in frame 54, the methodadvances to frame 56. In frame 56, the method includes regenerating theexhaust after-treatment device 24 using the modified baseline value forthe mass of soot. Following frame 56, the method may loop back to frame52. Once the method returns to frame 52, the monitoring of sensors 13,19, 36, 38, 40, and 42, as well as monitoring of the status of EGR valve44, may be resumed in order to determine the appropriate time for thenext regeneration of the after-treatment device 24.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A method for controlling regeneration of an exhaust after-treatmentdevice for an internal combustion engine in a vehicle, comprising:establishing a baseline value for a mass of soot collected in theexhaust after-treatment device, wherein the baseline value is athreshold mass of soot to be reached before regenerating theafter-treatment device, and is determined as function of a speed of theengine and a quantity of fuel entering the engine; modifying thebaseline value in response to an engine operating parameter to generatea modified baseline value, the engine operating parameter altering afuel-air ratio of a combustible mixture entering the engine; andregenerating the exhaust after-treatment device using the modifiedbaseline value.
 2. The method according to claim 1, wherein saidmodifying the baseline value is executed in response to an engineoperating parameter that alters the fuel-air ratio by varying a mass ofair entering the engine.
 3. The method according to claim 2, whereinsaid modifying the baseline value is executed in response to an engineoperating parameter that alters the fuel-air ratio by varying a mass offuel entering the engine.
 4. The method according to claim 3, whereinthe mass of fuel entering the engine is varied in one manner when theengine is operating in a steady state and in another manner when theengine is operating in a transient state.
 5. The method according toclaim 3, wherein the mass of fuel entering the engine is varied by anexhaust gas recirculation in the engine being turned on.
 6. The methodaccording to claim 1, wherein said modifying the baseline value isexecuted via a controller.
 7. The method according to claim 6, whereinthe controller is programmed with a look-up table that includes a rangefor the engine operating parameter.
 8. A system for controllingregeneration of an exhaust after-treatment device, comprising: aninternal combustion engine that generates an exhaust gas as a byproductof combustion and transfers the exhaust gas to the after-treatmentdevice; and a controller which is: programmed with an establishedbaseline value for a threshold mass of soot collected in the exhaustafter-treatment device before regenerating the after-treatment device,wherein the baseline value is determined as a function of a speed of theengine and a quantity of fuel entering the engine; and programmed tomodify the baseline value in response to an engine operating parameterthat alters a fuel-air ratio of a combustible mixture entering theengine; wherein the controller regenerates the exhaust after-treatmentdevice using the modified baseline value.
 9. The system according toclaim 8, wherein the baseline value is modified in response to an engineoperating parameter that alters the fuel-air ratio by varying a mass ofair entering the engine.
 10. The system according to claim 9, whereinthe baseline value is modified in response to an engine operatingparameter that alters the fuel-air ratio by varying a mass of fuelentering the engine.
 11. The system according to claim 10, wherein themass of fuel entering the engine is varied in one manner when the engineis operating in a steady state and in another manner when the engine isoperating in a transient state.
 12. The system according to claim 10,wherein the mass of fuel entering the engine is varied by an exhaust gasrecirculation in the engine being turned on.
 13. The system according toclaim 8, wherein the controller is additionally programmed with alook-up table that includes a range for the engine operating parameter.14. A vehicle comprising: an internal combustion engine that generatesan exhaust gas as a byproduct of combustion; an exhaust after-treatmentdevice configured to receive the exhaust gas and adapted to beregenerated; and a controller which is: programmed with an establishedbaseline value for a threshold mass of soot collected in the exhaustafter-treatment device before regenerating the after-treatment device,wherein the baseline value is determined as a function of a speed of theengine and a quantity of fuel entering the engine; and programmed tomodify the baseline value in response to an engine operating parameterthat alters a fuel-air ratio of a combustible mixture entering theengine; wherein the controller regenerates the exhaust after-treatmentdevice using the modified baseline value.
 15. The vehicle according toclaim 14, wherein the baseline value is modified in response to anengine operating parameter that alters the fuel-air ratio by varying amass of air entering the engine.
 16. The vehicle according to claim 15,wherein the baseline value is modified in response to an engineoperating parameter that alters the fuel-air ratio by varying a mass offuel entering the engine.
 17. The vehicle according to claim 16, whereinthe mass of fuel entering the engine is varied in one manner when theengine is operating in a steady state and in another manner when theengine is operating in a transient state.
 18. The vehicle according toclaim 16, wherein the mass of fuel entering the engine is varied by anexhaust gas recirculation in the engine being turned on.
 19. The vehicleaccording to claim 14, wherein the controller is additionally programmedwith a look-up table that includes a range for the engine operatingparameter.